Polyelectrolytes, particularly water-soluble synthetic anionic, cationic and amphoteric polymers, are commonly added to aqueous systems as active components of water treatment formulations or for other purposes. The control goal of most water-treatment programs is to maintain a special ratio of water treatment agent(s) to target specie(s) (for instance scaling ions, corrodents, contaminants and the like) in the water of the system and/or to minimize or maintain specified system consumption of active treatment component(s). The feed and other treatment-agent concentration controls are regulated to attain or maintain that ratio or specified treatment target dosage. The concentration fluctuations of a water treatment agent in an industrial aqueous system can defy conventional control means, preventing the target ratio or specified dosage from being uniformly maintained. Polyelectrolytes and other treatment agents may be lost to the aqueous system due to system consumption (selective losses such as treatment-activity consumption, deposit, corrosion, chemical and microbiological degradation processes and the like), hydraulic losses or removal (nonselective losses such as blowdown, drift and the like) and combinations of such phenomena. Treatment agents are replenished by feed of fresh formulation, but a precise replenishment requires a quantification of current in-system concentration.
Quantification of the in-system concentration of a treatment agent by quantification of all individual losses of the agent from the system may be an unreachable objective for most industrial systems. The extent of all such losses, and even the sources of all such losses, are seldom exactly known. Determination of the concentration of an active treatment component by conventional analysis techniques are often unsatisfactory. Such techniques commonly are not as beneficial as desired because of one or more of the following problems: background interferences from the system liquid or materials contained therein; bulky and/or costly equipment requirements; and inaccurate readings due to failures to detect one or more types of loss from the system, such as degradation or deposition within the system long delay time between when (manual) analyses are conducted and response (e.g., change in chemical feed rate) is initiated.
The target concentration of a polyelectrolyte and other active treatment components in the system may also elude system operators because of other operational abnormalities. Monitoring not only the current in-system concentration of a treatment agent but also its selective loss from the system would provide an indicator of treatment program performance.
If an in-system concentration of a polyelectrolyte and its selective loss from the system can be monitored, particularly if such monitoring permits both the concentration and the extent of loss to be quantified and if the monitoring is continuous, automatic control can permit polyelectrolyte-loss compensation, and a precise control over the in-system concentration and system consumption. If the extent of polyelectrolytes loss is instead only an inaccurate estimate, or if the monitoring for any reason fails to provide expeditious and reliable data on the concentration of a polyelectrolyte in an aqueous system, the responsive feed adjustment may result in a severe and deleterious underfeeding or a wasteful, and deleterious overfeeding of the treatment formulation. When for instance a polyelectrolyte is being added to an aqueous system to inhibit deposit formation and/or corrosion therein, a responsive feed adjustment that underfeeds the polyelectrolyte may be followed by deposit formation and/or corrosion within the system.
U.S. Pat. No. 4,783,314, John E. Hoots and Barry E. Hunt, issued Nov. 8, 1988, incorporated hereinto by reference, provides a method for monitoring a water treatment component by incorporating at least one fluorescent compound as a tracer into the treatment formulation to provide quantitative measurement/control of the treatment feed rate and performance. The concentration of a given fluorescent tracer in the aqueous system at a given point in time is generally determined by comparing the fluorescence emissivity of a sample from the system to a standard or a standard curve of fluorescent tracer concentration versus emissivity. Suitable fluorescent tracers for this method are substantially both water soluble and inert in the environment of the aqueous system in which they are used. This method at times herein is referred to as the "inert tracer" method.
U.S. Pat. No. 4,992,380, Barbara E. Moriarty, James J. Hickey, Wayne H. Hoy, John E. Hoots, and Donald A. Johnson, issued Feb. 12, 1992, incorporated hereinto by reference, describes a method for continuously monitoring a treating agent added to a body of water employed in a cooling tower by the characteristics of an inert tracer proportioned to the treating agent.
U.S. Pat. No. 5,128,419, Dodd W. Fong and John E. Hoots, issued July 7, 1992, incorporated hereinto by reference, describes a post-polymerization derivatization method for preparing polymers having pendant fluorescent groups. Polymers so marked or tagged may be monitored by fluorescence spectroscopy to determine the location, route, concentration at a given site and/or some property (for instance leachability) of these polymers and/or a substance in association with these polymers. As discussed therein, conventional techniques for monitoring polymers are generally time consuming and labor intensive, and often require the use of bulky and/or costly equipment. Most conventional polymer analysis techniques require the preparation of calibration curves for each type of polymer employed, which is particularly time consuming and laborious when a large variety of polymer chemistries are being employed. Conventional analysis techniques that determine analytically the concentration of a polymer's functional groups are generally not practical for industrial use, particularly when it is desired to monitor a polymer on a frequent or continuous basis, or when rapid results are needed. Indirect analysis techniques may provide results faster using simpler techniques, but in many instances even faster and/or more accurate determinations are highly desirable. If the fluorescent group incorporated into a polymer is derived from a highly fluorescent molecules, its presence will permit the monitoring of the polymer at concentration levels down to 0.1 ppm or less, even when the polymer is tagged with only one part by weight of the fluorescent group per 100 parts by weight of polymer. The post-polymerization is a (trans)amidation derivatization of preexisting polymers having carbonyl-type pendant groups, including pendant carboxylic acid, carboxylic acid ester and amide groups. This post-polymerization derivatization method is exemplified in U.S. Pat. No. 5,128,419 using a variety of starting-material polymers, including acrylic acid homopolymers, acrylic acid/acrylamide copolymers, acrylic acid/acrylamide terpolymers with sulfomethylacrylamide, vinyl acetate, acrylonitrile and methacrylic acid. At times herein the terminology of "tagged polymers" are used to refer to these polymers and/or other pendant-fluorescent-group-containing polymers prepared by other methods.
Prior to the above-mentioned inventions that utilize fluorescence spectroscopy or other methods to provide to the water treatment field simple, accurate and rapid monitoring techniques, the fastest technique for on-site monitoring of polymeric treatment components was the "PA-1/PA-2" polyacrylate turbidity test. This turbidity test technique determines the concentration of polymers having pendant carboxylic acid groups based on a reaction between the carboxylic acid groups and a cationic organic compound. The reaction product forms as a suspension of insoluble colloidal particles and the measure of polymer concentration is the reaction mixture turbidity. At times herein this PA-1/PA-2 polyacrylate turbidity test is referred to as merely "the turbidity test".
The turbidity test and fluorescence analysis of tagged polymers are both analytical techniques that are directed to the polymer itself rather than on an associated inert tracer. The turbidity test is, however, limited in selectivity and thus prone to interferences from substances other than the polymer in question. For instance, nonpolymeric surfactants and other organics can also produce turbidity under test conditions, and color and/or turbidity might be present in the water sample as obtained. The turbidity forming reaction can be interfered with by inorganic ions or other sources of turbidity in the water. The turbidity test is also limited in its industrial application by the time and/or technique dependence of its results (result variations occurring with the operator's technique or the length of time before the turbidity reading).
The monitoring of fluorescent tagged-polymers is of course limited to polymers that have been provided with pendant fluorescent groups that endure under the conditions of the aqueous system. A given polymer may not be commercially available in tagged form, or may not be readily tagged.
A method for determining the concentration of polysulfonate and/or polycarboxylate compounds in a solution sample by adding a metachromatic dye thereto and then comparing the solution's absorbance to that of standard solutions is described in U.S. Pat. No. 4,894,346, Myers et al., issued Jan. 16, 1990. Metachromasy is the color-changing phenomenon of certain dyes upon interaction or complexation with a polyelectrolyte. The color of dyes is derived from their ability to absorb light in the visible region of the spectrum, between about 400 and 800 nm. Absorption is caused by electronic transitions in the molecules and can occur in the visible region only when the electrons are reasonably mobile. Mobility is encouraged by unsaturation and resonance. The main structural unit of a dye, which is always unsaturated, is called the chromophore, and a compound containing a chromophore is called a chromogen. Auxochromes, such as hydroxyl, amino and carboxyl groups, are substituent atoms or groups that effect the intensity and at times the absorption band of a chromophore. The hue, strength and brightness of a dye depend on the entire light-absorbing system of the dye molecule. In general, for a given type of dye, extension of the unsaturated system, which increases the opportunities for resonance, shifts the absorption of light toward longer wavelengths. Then the color that is absorbed progresses across the visible spectrum from violet to purple, and the color seen by the human eye is the color complementary to that absorbed. A metachromatic color-change is seen when an ionic dye interacts with an oppositely-charged polyelectrolyte in solution. The interaction or complexation that produces the color change is believed to result from the aggregation of dye molecules as a consequence of three types of forces, i.e., the electrostatic attraction between an ionic dye and oppositely-charged sites on the polyelectrolyte, the hydrophobic attraction of dye molecules to nonpolar regions of a polyelectrolyte, and the pi-electron interaction between adjacent or closely proximate dye molecules. The color change results from a shift in a dye's maximum absorbance wavelength (absorptive metachromatic shift).
Some metachromatic dyes are fluorescent. It has been observed that the fluorescence intensity of certain polycyclic aromatic reagents increased when they interacted with various cationic or nonionic polymers, and a secondary method utilizes this phenomenon and the affinity of the resulting complexes to biological polyanions to form ternary complexes for use in fluorescence microscopy, flow cytometry and other quantitative method, as described in European Patent No. 0 231 127, A. L. Wu, 1987.
Another quantitative method employs the complexing interaction between an anionic reagent and a cationic polyelectrolyte (but not the metachromatic spectral change, if any), whereby a complex that can be extracted with a hydrophobic solvent is formed, as is described in Anal. Chem., D. P. Parazak, C. W. Burkhardt and K. J. McCarthy, Vol. 59, pages 1444-1445, 1987.
Monitoring a polymeric treatment agent using both an associated inert tracer and a quantitative analytical technique permits the determination of the system consumption for the polymer and indicates the severity of the operating conditions. It also permits-a "performance based" polymeric-treatment in-system concentration control method. The polymer feed or other polymer-concentration control is correlated to selective system consumption for the polymer and compensates also for nonselective polymer removal by hydraulic losses (removal with blowdown, drift and the like) and any operational abnormalities (changes in pumping rates of chemical feed pump and the like). Such dual monitoring would permit differentiation between selective and nonselective polymer losses. As the severity of operating conditions increases/decreases (system consumption), the target polymer concentration can be concomitantly increased/decreased. Such monitoring and in-system concentration control methods are of course restricted by the requirements of, and limitations inherent in, the quantitative analytical technique chosen.
It is an object of the present invention to provide a method for monitoring and/or controlling polyelectrolyte losses and/or dosages in an aqueous system, particularly on a continuous basis. It is an object of the present invention to provide a method for monitoring and/or controlling polyelectrolyte concentrations in an aqueous system that is substantially independent of an operator's laboratory technique. It is an object of the present invention to provide a method for monitoring and/or controlling polyelectrolyte concentrations in an aqueous system that provides a response that is substantially linear to polyelectrolyte concentration. It is an object of the present invention to provide a method for determining the system consumption for a polyelectrolyte that includes a selective quantitative analytical technique that is not limited to tagged or other specialty polymers. It is an object of the present invention to provide a polyelectrolyte "system consumption" in-system concentration control method that includes a selective quantitative analytical technique that is not limited to tagged or other specialty polymers. These and other objects of the present invention are described in more detail below.